For example, U.S. Pat. No. 5,769,391 (JP-A-11-500509) discloses a fuel injection valve having a solenoid valve including a stationary core, a movable core, a valve element, and a coil. When the coil is energized, the stationary core and the movable core therebetween generate magnetic attractive force to manipulate the valve element together with the movable core so as to control communication in a fluid passage for intermitting fuel injection. In U.S. Pat. No. 5,769,391, a movable core side magnetic portion surrounds an outer circumferential periphery of the movable core. The movable core side magnetic portion and a stationary core side magnetic portion therebetween define a magnetism throttle. The movable core side magnetic portion, the stationary core side magnetic portion, and the magnetism throttle are integrated into one component. In U.S. Pat. No. 5,769,391, the magnetism throttle restricts the movable core side magnetic portion and the stationary core side magnetic portion from magnetically short-circuiting therebetween when a coil is energized. Thus, the movable core and the stationary core generate magnetic attractive force in a gap therebetween.
In U.S. Pat. No. 5,769,391, the magnetic throttle is formed from a magnetic material, whereby the movable core side magnetic portion and the stationary core side magnetic portion can be restricted from magnetically short-circuiting, nevertheless magnetic flux may leak through the magnetism throttle. As a result the magnetic attractive force between the movable core and the stationary core may decrease.
Alternatively, it is conceivable to provide a nonmagnetic portion, instead of the magnetic throttle, which is formed from the magnetic material. In this case, the nonmagnetic portion is provided between the movable core side magnetic portion and the stationary core side magnetic portion to surround radially outside a gap, which is defined between the movable core and the stationary core. In the present structure, the nonmagnetic portion is capable of restricting the movable core side magnetic portion and the stationary core side magnetic portion from magnetically short-circuiting therebetween.
However, in the present structure, an eddy current may arise in the nonmagnetic portion when the coil is de-energized and magnetic flux quickly reduces in the gap. When an eddy current arises in the non-magnetic portion, which is located radially outside the gap, magnetic flux may be induced in the magnetic portion in the vicinity of the gap. Consequently, magnetic attractive force between the stationary core and the movable core may be retained for a long period. Consequently, response of the valve element of the solenoid valve may be impaired when the coil is de-energized.